Pressurized metered dose inhalers (“pMDIs”) are common in the industry, as are conventional MDI actuators that are based on “two-orifice-and-sump” designs. Unfortunately, their commonality is accompanied by their common disadvantages: high spray velocity and inadequate particle size distribution control, which results in poor drug delivery to the patient. It is postulated that high spray velocity is one of the lead causes of high oropharyngeal drug deposition (Newman S., (2005) “Principles of Metered-Dose Inhalers”, Respiratory Care, Vol. 50. No. 9. pp. 1177-1190). Previous attempts at solving this problem are evidenced by the use of spacers to reduce spray velocity (e.g. U.S. Pat. No. 4,972,830). However, spacers are bulky, and drug deposition within the spacers leads to a decrease of actual drug delivered to the patient. Other methods for slowing plume force include introducing complicated baffles or bluff bodies into the device nozzle or mouthpiece, or introducing a flow control/mixing chamber into the mouthpiece (e.g. U.S. Pat. Nos. 6,615,826 and 6,527,151). These methods, however, also have the propensity to increase drug deposition in the mouthpiece at the site of the baffles, bluff bodies, or other airflow obstructions.
Modifying the aerosol generation mechanism itself using a vortexing chamber produces a low plume force spray, as described in U.S. Pat. No. 6,418,925, which is incorporated herein by reference. According to the present invention, modifying the actuator design by using a flat or protruding nozzle face, as opposed to a “standard” concave-conical nozzle face (common in the industry) and a diverging mouthpiece insert further reduces drug deposition on the nozzle face, the device mouthpiece, and the throat of the patient.
Applicants have discovered that a flat or protruding nozzle face affects the dynamics of the aerosol flow at the nozzle orifice, which in turn affects the particle size distribution in the aerosol spray leaving the orifice. Upon actuation using the present invention, the drug-propellant mixture from the canister enters the vortex chamber of the nozzle of the present invention at an angle. The mixture flows along the periphery of the chamber which sets up a swirling motion, until the mixture leaves the device via an axial exit orifice at a decelerated velocity. The nozzle face geometry discovered by the applicants restricts the extent as well as spread of unvaporized drug-propellant mixture around the nozzle orifice, thus limiting drug deposition around on the nozzle face. The mouthpiece insert works to further decelerate the spray.